The invention relates to a process and apparatus for manufacturing resin-impregnated, reinforced--particularly fiberglass reinforced--articles in such a way that the styrene or other volatiles in the reinforcing structure or "laminate" cannot escape into the surrounding atmosphere.
A technique used in the production of fiberglass parts for many years has become known in the art as "preforming". In this method an auxiliary mold revolves in the center of a chamber. The auxiliary mold is made of a screen similar to the type used for screen doors and it has the approximate shape of the matched die mold which is used to form the final part. A vacuum fan exhausts the area behind the auxiliary mold while it rotates in the center of the chamber. Chopped fiberglass is blown into the auxiliary mold and because of the vacuum is evenly distributed across the face of this mold. A fine mist of some type of adhesive, usually a cross linking resin emulsion is sprayed simultaneously onto the part. After the desired thickness of chopped fiberglass has been obtained the cutter and spray system stop and the mold is baked under infrared lights or some other heat source until tack free.
When the baking process has been completed the fiberglass mat now formed in the shape of the auxiliary mold is removed easily from the screen. This "preformed" mat is then transferred to the die mold onto which a measured quantity of catalized resin is poured. The male and female molds are pressed together under great pressure. The resin is forced through the thousands of cut strands of fiberglass until it has impregnated all vacancies. Heat is then often applied to the mold surfaces and the resin cures quickly. The matching mold sections are then pulled apart and the finished fiberglass part is produced smooth on both sides.
This known preforming technique has the disadvantage that it requires the use of expensive matched die molds usually made of metal. In addition it is subject to the drawback that the odorous resin fumes escape into the work atmosphere while the molds are open.
Another technique for producing fiberglass parts is known as "vacuum bagging". In the vacuum bag process a single cavity mold is employed and a normal fiberglass part is laid-up or sprayed-up in this mold. In this process the resins of necessity must be catalyzed very slowly to allow for the completion of the normal laminating time plus the process of the vacuum bagging.
In the vacuum bagging technique a fiberglass part is produced in its entirety. Then a gum-like tape is applied around the entire periphery. A sheet of thin plastic substance is draped over the entire laminate. This sheet of plastic adheres around the edges to the gummed vacuum tape. A vacuum hose is placed through the vacuum tape and sealed so that when a vacuum source is connected to this hose a vacuum is developed inside the vacuum bag, the latter being formed by the combination of the mold and the plastic sheet. As the vacuum continues, atmospheric pressure pushes down on the sheet and presses it against the wet fiberglass laminate. Excess resin is squeezed from the part and captured by absorption strips placed at various points about the laminate.
The vacuum is allowed to remain on the part until the resin has hardened. The plastic sheet is then simply removed from the part as there is no adhesion between resins and this type of covering. A very strong, even and smooth fiberglass part is produced this way and most such parts which call for considerable mechanical strength, such as aircraft parts and missile parts, are manufactured with this technique using epoxy resins. However, the open resin laminate which is present, until the vacuum bag is put in place, gives rise to the presence of resin odor in the work environment. Further, the process is messy and human contact with the resin is inevitable.
U.S. Pat. No. 2,913,036 to Smith shows a modification of this vacuum bagging technique in which laying-up or spraying-up of the laminate is avoided. In the arrangement disclosed in this patent one or more layers of fiberglass mat or fiberglass cloth is laid on top of a large upwardly convex mold. On top of this fiberglass in turn an impermeable sheet of plastic material or the like is laid and the periphery of this sheet is joined in airtight fashion to a flange at the bottom of the mold. A vacuum line is connected to several openings in the top of this sheet and a vacuum chamber is formed in this manner. A resin line is likewise introduced into this chamber, namely into a circumferential trough at the bottom thereof, and a plurality of hollow members of relatively rigid materials which are unconnected to any of the other elements of the assembly are also placed in this chamber. These members form a network of veins or arteries which extend throughout the aforementioned chamber as an aid in the distribution of the resin. The members may be embedded between layers of fiberglass fabric in the molded article; in that case the aforementioned arteries themselves become a part of the final casting and they typically appear in the form of reinforcing ribs.
In the apparatus disclosed in the Smith patent then, the resin which is introduced into the vacuum bag at the base of the upwardly convex mold, must be drawn up by the vacuum, initially in a straight vertical direction and then vertically and radially, into the laminate against the action of gravity. It is clear, therefore, that with such a design a uniform distribution of the resin throughout the entire extent of the laminate, if at all possible, is extremely difficult to attain.
A further example of a vacuum bag technique is described in British Pat. No. 944,955.